Purification of vat dyestuffs



Patented Sept. 27, 1949 PURIFICATION OF VAT DYESEIEFFS 7 Mario Scalera, Somerville,1N-; J}, assignor to American Cyanamid Company,

.a corpor'atio nof Maine N Drawing. Application March 23,"1944 ,;l

Serial No. 521,847.

This invention relates to'a new andimproved process for producing-pure vat dyestufis =containi-r-ig the ring-system Dyestufisnontain-ingithe above iring systernzare anximportant iclass aof vat dyestufts, dyeing textiles and fiber-s. dankzgreencto olive :to :grayashades; and shown-exceptional. alight .fastness: .The com monprocedure for. preparing athesezdyestufis is 17.9 react :a bzl halogen- :ben-zanthrone'with :anpalphaaminoeanthraquinone, .;foll0wed by an; alkaline fusion; The-purity: of the :dyestufttproduced (dopends primarily .omt-he .pnrityzof zth'e halogenated benzanthrone .used; land i'as *itlis :not :easy :to (PIG-2 pare the halogen ben-zanthrones 1in: a mum 'EfOlZIIl with goodi yields the ;.usual processeresultsin'ea crude product which:isz-qqnite-iimpure. ThBiGOSt of purification. iszhighlandzas LitJhasi'been-a Ldififilllt and expensivezmatter in the: past .ztoapurity" {the bzl-chloro benzanthrone used as::rawzmaterialrthe cost 20f athe purified final dyestufis has iremained quitehigh; The impurecompound-doesrnot have the brightness. and shade ldesired rand: :purificas tion is, therefore, necessary.

:Dyestufis of thea-typecztorwmchmheipresentiim vention relates cannot :be zpurified, by ;.a.- method which is commonly used 1 with otherxaanthra i quinone dyestuffs, namely oxidation in aqueous suspension, because 'tliistreatment tends to ruptureathe ben-z-ring,and=';produce phenanthridones. Ithas been proposedtopuriiy .the dyestufisvby fractional precipitation-of their sulfates-Hilton! sulfuric acid of -.80-85%-strength.. This ,process is capable: ofiproducing .a :dyestufi of reasonably. goodpurity. However, the process .is penito ery, serious .idisadvantages. Ther-dyestuffs are (quite sensitive :to concentratedsulfuric-acid There is a tendency towards sulfenatiomor.-;decomposition-, possibly by oxidation. Therefore, the precipitate. tion :has to he carried: out sat-1a: very low {temperature, about- 1C. andnaven thenithe yieldsare-icon. siderably lowered; Another practical =disadvantage-is due tothe natureiofathe precipitated-dye stuff sulfates. Unfortunately they come-:dewrrzin a slimy .finely crystalline formwhich presents great -itechnical-zdilficulties in filtrationt- I tures.

The present invention efiects a technically excellent purification of the class of dyes referred to which is free lfrom the disadvanges described above. The method of th present invention depends on precipitating the leuco form of the dyestuffs by salting out in aqueous solutions. The impurities remainin :solution and the pure dyestuffs may be recovered from the filter cake by reoxidation.

The general pnocedureiof saltin out leuco vat dyestufis is not a new th'ingrin vat dye chemistry. The process has been 2 used with certain other vat dyestuifs which give leucoscompounds that are sparingly soluble in water or weak salt solutions. It would ordinarily be expected that the processwould be 'rna-ppliable-'-to-thepurification ofthe' dyestuifs-to wliiclithe *pres'ent invention-is directed because=-*their **leucomornpounds are in general quite' solublein waiter and concentrations as high as 10-15% of sodium chloride are neces sary in order to effect precipitation. Under these conditions the natural presumption would be that many of the impurities present in the crude dyestufi Wouldalso be precipitated, and that probably the recovery of pure dyestuiT would be low. surprisinglyenough I have found that with the dyestufis' to which/"the present invention is directed it is possibl toiisolate the leuco form of the dye inqa pure stateain substantially quantitative recovery; even when crude deystufis are treated which have been prepared 'zfrom halogen benzanthrones of very low purity (-40e50%). I do not know why the impurities associatedowith these particular dyestuffs are not precipitated by the salting out procedure. The exact nature of these impurities is not fully known, but apparently without exception they show an extraordinary solubility in quite concentrated salt solutions.

it '-is -'possib1--to* carry orrt the-process of the present invention in various-modifid ways,and it is an advantage of the present invention that the most satisiactoryunodification for a particular technical installation may readily be chosen. One very satisfactory procedure is to reduce the crude dyestufipreferably in the form of a paste by means of sodium; hydrosulfite and caustic alkali to produce a clear van -the reduction being efiected preferably attslightlytelevated tempera- The salting out agent such as, for example, sodium chloride is: then added to cause complete precipitation "of the lenconcon pourld. In many cases the latter separates out inaalm st quantitative yields, free from impurities; but it separates out in a crystalline fnrmrwhichfis readily filtered. Filtration and washing of the filter Cake prqceedrfilfinaicormentionalzdines andzarezn'ot critical-r Anotheranod-ification ni Ethel present invention which presentseeonsiderableiadvantages :imz-olyes' the combined purification and formation of the dyestuff. The ring closure of the dyestuif is normally effected by fusion in alcoholic caustic alkali. This results in the production of the leuco dyestuif and the salting out agent may be added directly to the drowned fusion melt, which is then filtered and the purified leuco dyestuff isobtained directly without intermediate isolation of the crude dyestufi. Yields are, excellent and a considerable saving in equipment and labor in made possible. This modification, wherever applicable, may, therefore, be considered as a preferred modification of the present invention.

The dyestuffs which may be purified by the process of the present invention are, for instance, the parent compound of the formula:

its simple substitution products, such as halogen, alkyl, and alkoxy derivatives; its amino substitution products, including substituted amino products, such as the compound of the formula:

and its acylamino products,such as the compound of the formula: I

The leuco compounds may be produced by any known means, such as by the alkaline fusion of the intermediate benzanthronyl-anthraquinonyl amines containing the ring system:-

as already mentioned above; or by alkaline reduction of the dyestuffs themselves, for instance with sodium hydrosulfite and alkali.

The salting out of the leuco compound proceeds in accordance with the normal laws, that is to say a common ion enhances the salting out effect. The leuco compound is usually in the form of its sodium salt when sodium is the chosen alkali, and in such case the compound used for salting out should be a readily soluble sodium compound. Typical compounds are sodium chloride, sodium carbonate, or sodium hydroXide. Salting out of the leuco dyestufi in the form of its potassium salt is less satisfactory in most cases because of the high solubility of the potassium compound. Where feasible it would require the use of potassium salts instead of sodium salts. With most of the dyestuffs the sodium salt of the leuco can be salted out more economically and this is the preferred procedure. It is an advantage of the present invention that the precipitation is not at all critical with respect to temperature. Useful results are obtainable at any temperature between 0 and C. The process proceeds most eifectively, however, between 50 and 90 C. and this constitutes the preferred range. At lower temperatures the precipitation of the leuco compound is in the form of finer less readily filterable crystals, while higher temperatures make it very difiicult to avoid accidental oxidation of the leuco compounds by air. The precipitation must be carried out in a strongly alkaline medium in order to avoid hydrolysis or rearrangement of the leuco form of the impurities which might result in their precipitation and hence in the production of an impure product. However, the exact alkalinity is not critical, although I prefer to operate at a pH above 12.

The invention will be described in greater detail in conjunction with the following specific examples. The parts are by weight.

Example 1 Fifty-five parts of the dyestuff resulting from alcoholic potash fusion of crude bzl-benzanthronyl-l-amino-anthraquinone (prepared by reacting the technical bzl-bromo benzanthrone, obtained by bromination of benzanthrone in aqueous suspension, with l-amino-anthraquinone) are suspended in 2500 parts of water. parts of caustic soda solution of 40 B. and 50 parts of commercial sodium hydrosulfite are added.

The vat is heated to 70 C. and treated with an additional 120 parts of 40 B. caustic soda and 50 parts of sodium hydrosulfite. While maintaining the same temperature, there are added 1000 parts of concentrated salt solution (25% sodium chloride by weight). The resulting slurry is allowed to cool to- 25 C. and filtered.

The liquor from the. filtration of the leuco compound described aboveis deep-,-black-brwn in color. On aeration and filtering it; gives -12 parts of a dark compound which :dyes cotton from the vat in dull grayisha-olive'to brownisholive shades.

Example 2 Fifty-six parts ofthe same crude dyesturf usedin -the preceding example, preferably inthe form of a wet filler cake, are suspended in 3000-parts of water and vatted by the addition of 240parts OflO 'B. caustic soda' solution and-100 parts of sodium hydrosulfite. The resulting vat is heated to 70-" C. and treatedwith an additional 700 parts of- 40- B.. caustic soda solution-,--preheated to the same temperature.

The slurry is cooled to C. and filtered. The dark, blue-black presscake is washed with a solution of caustic soda of approximately 12 B., containing a little sodium hydrosulfite, until the washings come through clear pale blue.

There are obtained 361-40 parts of a very pure dyestufi substantially identicalv to that described in Example 1. From the filtered vat solution the olive colored byproduct described in the preceding example may be obtained by aeration and filtering.

Example 140 parts of crude dyestuff 0f the.formll1a:

(obtainable b qzthecreacti-on oi 2 mols. of alpha aminozanthraquinonewith'1 mol. of' 6, bzl-dibroe mo -benzanthrone, followed by 'fusion with alcoholic potash), in the form of a 20% presscake, are slurried in 5000 parts of water and vatted bytheladdition ofg'mil, parts of caustic soda and 200 parts of sodium hydrosulfita;

The.clearvat' isheated 110.70". C. and. 930 parts of-sodium-chloride are addedxat-tl'ie same tem-' perature: over 30 minutes;v The: solution is. al-. lowed to cool to 25 C. and filtered.

The presscake' contains a dyestuff which dyes from-:the .vat olive shades which are substantiallyggreener-and brighter than those obtained from the crudelstarting materia1:.:.

Examples! '50 *par-ts of-- the benzanthronyl amino di-anthrimid'e of theiormu-la:

(obtainable by the reaction of 5-amino-1,l"-di' anthrimide with bzl=bromo benzanthrone in.ni-'

trobenzene; in th presence of an acid' bin'ding substance and a copper catalyst) are heated'in a'meltof 500"parts of caustic potash and 250 parts'of methanol 'under. reflux untilring closure-occurs.

Theresulting slurryis poured into 3600 parts of water, parts of sodium hydrosulfite and 405) parts of sodium chloride are'added thereto, and

the-slurry iscooled to 25 C. and filtered. The presscake'is washed with 15% salt brine contain-' inga small-amount of hydrosulfite until the washings are colorless.

The cake is -thenslurried in water; aerated-fil tered and washed free ofalkali. The dyestuff thus obtained dyes cotton in pure gray shades whichxrare; considerably: brighter than those obtainable by the same,- rfusion .when the. purificaa tion through the leuco compound is omitted.

In the above Example 4, the mixture formed by combining the potash melt with the water,

the sodium hydrosulfite and the sodium chloride contained a total ofabout 4% by weight of combined sodium.

Examplefi 91 parts of the dyestufi of the formula:

(obtainable by the reaction of bzl-chloro benzanthrone with 1-amino-5-methoxy anthraquinone in boiling nitrobenzene in the presence of soda ash and cupric chloride, followed by ring closure in alcoholic potash) are vatted in 4500 parts of water by the aid of 450 parts of caustic soda and 130 parts of sodium hydrosulfite.

The solution is heated to 70 C., 600 parts of sodium chloride are added, and the slurry is filtered at 60 C. and washed with warm 10% salt brine.

The compound dyes cotton in green shades. From the filtrate of the leuco compound there can be isolated by aeration 5-10 parts of a byproduct dyeing cotton dull olive shades.

Example 6 180 parts of alpha amino anthraquinone and 200 parts of the product resulting from chlorination of benzanthrone in concentrated sulfuric acid are reacted together in boiling nitrobenzene in the presence of sodium carbonate and cuprous iodide for 20 hours.

The reaction mixture is cooled, filtered, the product washed with nitrobenzene and steamed free of solvent. There are obtained 275-280 parts of a brownish violet body which is a mixture of various products.

50 parts of this material are charged into a melt of 250 parts of caustic potash and 125 parts of methanol and heated at 150-155 C. for 1 hour. 250 parts of water are added to the melt while distilling out the alcohol. The resulting solution is poured into 2000 parts of water, and 10-20 parts of sodium hydrosulfite (to forestall air oxidation) and 400 parts of common salt are added.

The slurry is cooled, filtered, and the residue washed with a solution containing 15% sodium chloride, 5% caustic soda, and 1% sodium hydrosulfite, until the washings are clear, faint bluishpurple.

From the presscake can be isolated 15-16 parts of the pure dyestufi described in Examples 1 and 2, or a yield of 30% to 31% of the theoretical.

The fraction soluble in the reducing liquor may be recovered by aeration. It amounts to 32-33 parts and dyes cotton bluish-gray shades.

Example 7 50 parts of technically pure benzanthronyl-anthraquinonylamine of the formula:

(obtained by reacting bzl-chloro benzanthrone, prepared by chlorination of benzanthrone in 92% phosphoric acid according to my copending application Serial No. 527,846, filed March 23, 1944, now Patent No. 2,418,318, with l-amino anthraquinone) are introduced at 150 C. into a melt of 250 parts of caustic potash in 125 parts of methanol.

The resulting black slurry is heated to reflux 8 (158-159 C.) for 1 hour and then 250 parts of water are cautiously added while allowing the alcohol to distill out. The resulting solution is diluted with an additional 250 parts of water and is poured into 2000 parts of water to give a clear,

deep blue solution. 10-20 parts of sodium hydrosulfite are added, if necessary, to prevent oxidation by the air; then the solution is heated to 85 C., and 400 parts of common salt are added slowly at this temperature. The resulting slurry is cooled, filtered and washed with brine solution (containing a small amount of dissolved caustic soda and hydrosulfite) until the drippings are pale blue and translucent.

15 The presscake is suspended in 2000 parts of water, aerated, boiled, filtered and washed to neutrality. There are obtained 43-44 parts of the green dyestuff of the formula:

and leuco derivatives of the halogen substituted, alkyl substituted, alkoxy substituted, amino substituted, anthraquinonylamino substituted, and acylamino substituted derivatives of said dyestuff, which comprises the steps of forming a strongly alkaline vat of said leuco derivative, mixing with said vat an amount of a soluble ionizable sodium compound sufficient to form a precipitate of a leuco derivative of said dyestufi and also to form a mixture containing a total of at least about 4% by weight of combined sodium, and recovering said precipitated leuco derivative in substantially pure form.

2. A process according to claim 1, in which the precipitation is effected at a temperature between 50 and 90 C.

3. A process according to claim 1, in which the precipitation is efiected in a vat having a pH of at least 12.

which comprises the steps of forming a strongly alkaline vat of said leuco derivative, mixing with said vat an amount of a soluble ionizable sodium compound suificient to form a precipitate of a leuco derivative of said dyestuif and also to form a mixture containing a total of at least about 4% by weight of combined sodium, and recovering said precipitated leuco derivative in substantially pure form.

5. A process according to claim 4, in which the precipitation is effected at a temperature between 50 and 90 C.

6. A process according to claim 4, in which the precipitation is effected in a vat having a pH of at least 12.

7. A method for the purification of a watersoluble leuco derivative of a vat dyestulf of the following formula:

OO O which comprises the steps of forming a strongly alkaline vat of said leuco derivative, mixing with said vat an amount of a soluble ionizable sodium compound suficient to form a precipitate of a leuco derivative of said dyestuif and also to form a mixture containing a total of at least about 4% by weight of combined sodium, and recovering said precipitated leuco derivative in substantially pure form.

8. A process according to claim '7, in which the precipitation is effected at a temperature between 50 and C.

9. A process according to claim '7, in which the precipitation is efiected in a vat having a pH of at least 12.

10. A method for the purification of a watersoluble leuco derivative of a vat dyestuff of the following formula:

which comprises the steps of forming a strongly alkaline vat of said leuco derivative, mixing with said vat an amount of a soluble ionizable sodium compound sufi'lcient to form a precipitate of a leuco derivative of said dyestuff and also to form a mixture containing a total of at least about 4% by weight of combined sodium, and recovering said precipitated leuco derivative in substantially pure form.

11. A process according to claim 10, in which the precipitation is effected at a temperature between 50 and 90 C.

12. A process according to claim 10, in which the precipitation is efifected in a vat having a pH of at least 12.

MARIO SCALERA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 995,936 Wolff June 20, 1911 1,150,863 Just Aug. 24, 1915 1,828,592 Bommer Oct. 20, 1931 1,961,921 Honold June 'I, 1932 1,935,724 Neresheimer Nov. 21, 1933 2,091,102 Peck Aug. 24, 1937 2,150,109 Stallmann Mar. 7, 1939 2,212,029 Lulek Aug. 20, 1940 2,251,566 Graham Aug. 5, 1941 2,312,462 Wuertz Mar. 2, 1943 

